The Minnesota Department of Agriculture (MDA) confirmed the presence of emerald ash borer (EAB) in Prior Lake in August, 2015.  EAB is an insect that attacks and kills ash trees and is spread through the transport of firewood. The adults are small, iridescent green beetles that live outside of trees during the summer months. The larvae are grub or worm-like and live underneath the bark of ash trees.  Emerald ash borer larvae kill ash trees by tunneling under the bark and feeding on the part of the tree that moves nutrients up and down the trunk.

What to do if you have a confirmed infestation of EAB

OPTION 1 - Remove the tree
Tree removal or pruning should be completed during the EAB dormant period, October 1 through May 1. Material that is disturbed during the EAB active period may release adults into a previously un-infested area. By postponing removals until the dormant period, you can help reduce the risk of EAB spreading. If a tree or branch is cut and properly disposed of during the dormant period, any adult EAB or larvae that may exist in the ash material will be destroyed when the wood is destroyed.

If tree removal is necessary, then remove at least the outer 1” of bark/wood on site, contain it to minimize spreading, and transport it to the nearest facility that can properly dispose of the material. 

OPTION 2 - Treat the tree
It's best to begin using insecticides while ash trees are relatively healthy.  By the time most people notice canopy dieback, EAB has already caused considerable injury to the vascular system of the tree.  If there is more than 30% canopy loss, treatment is usually not effective and it's too late to save the tree. Options to treat the tree include soil injection or drench, trunk injection, systematic bark spray and granules.

Two life stages of EAB are targeted by treatments: adult beetles and young larvae. Insecticides only work while they are present in the tree, and products are generally labeled for 1-2 years of effectiveness.  Treatment will need to be repeated if EAB is still present when the effective period ends.

Contact a certified arborist to evaluate treatment options.  If hiring a professional, ask if they are licensed as a Commercial Pesticide Applicator for category E: Turf and Ornamentals.

Helpful Resources

Map of EAB in Minnesota
MN Department of Natural Resources EAB Information
MN Department of Agriculture EAB Information